1. Field of the Invention
The present invention relates to a pressure sensor having a tubular member inserted into an opening of a housing thereof, the tubular member including a sensing section located at one end thereof, a pressure transmission member located in a hollow space thereof, and a pressure-receiving diaphragm located at the other end thereof.
2. Description of Related Art
A pressure sensor of such type is disclosed in Japanese Patent Application Laid-open No. 2006-208043 filed by the same inventor of the present invention. FIG. 7 is a schematic cross-sectional view showing a major part of the pressure sensor disclosed in this patent application.
As shown in this figure, this pressure sensor includes a first hollow tubular member 1 having a metal stem 20 as a main body thereof. The first tubular member 1 includes a sensing section 22, 30 located at one end portion thereof which outputs an electrical signal indicative of a pressure applied thereto, and an opening section 21 formed at the other end thereof. The first tubular member 1 further includes a thin-walled section at the one end portion thereof which serves as a diaphragm 22 and on which a sensing element 30 is provided. The diaphragm 22 and the sensing element 30 constitute the sensing section 22, 30.
This pressure sensor further includes a second hollow tubular member 2 having a metal case 15 as a main body thereof. The second tubular member 2 includes an opening section 16 formed at one end portion thereof, and a pressure-receiving diaphragm 14 located at the other end portion thereof. These first and second tubular members 1, 2 are fixedly connected to each other at their opening sections 16, 21 such that their hollow portions communicate to each other.
More specifically, the opening section 21 of the first tubular member 1 is inserted into the opening section 16 of the second tubular member 2, and the first and second tubular members 1, 2 are integrally connected to each other by laser welding at a weld portion K1, so that they form a single tube.
A pressure transmission member 17 is housed in a hollow space of the tubular members 1, 2 integrally connected to each other. One end of the pressure transmission member 17 is located on the side of the sensing section 22, 30, and the other end is located on the side of the pressure-receiving diaphragm 14. This pressure sensor further includes a housing 10 having an opening section 11 formed at one end thereof. Although not shown in FIG. 7, the housing 10 contains therein a circuit board and wires for processing a signal outputted from the sensing element 30.
The tubular members 1, 2 integrally connected to each other are inserted into the opening section 11 to be supported by the housing 10 such that the sensing section 22, 30 is located inside the housing 10, and the pressure-receiving diaphragm 14 projects from the housing 10. The first tubular member 1 and the housing 10 are fixed to each other by laser welding at a weld portion K2.
In the pressure sensor having the above described structure, the pressure applied to the pressure-receiving diaphragm 14 is transmitted to the sensing section 22, 30 through the pressure transmission member 17. The resultant distortion of the diaphragm 22 is converted into an electrical signal by the sensing element 30.
Ideally, all the center axes of the first tubular member 1, second tubular member 2, and housing 10 should align with each other and extend in the same direction (in the vertical direction in FIG. 7).
However, since the first and second tubular members 1, 2 project form the opening section 11 of the housing 10, an axial misalignment in which their axes are inclined with respect to one another may occur in these members.
The pressure sensor of the type described above is mounted to a pressure-sensing object such as a vehicle engine in such a state that the tubular members 1, 2 and the housing 10 are inserted into a hole formed in the engine. Accordingly, if the axial misalignment is excessively large, there is a fear that the pressure sensor cannot be mounted to the engine.
Since there is some clearance between the opening section 11 of the housing 10 and an outer periphery of the first tubular member 1 inserted into the opening section 11, and also between an inner periphery of the opening section 16 of the second tubular member 2 and an outer periphery of the opening section 21 of the first tubular member 1 inserted into the opening section 16, there is a possibility that the first tubular member 1 is inclinedly welded to the housing 10, and the second tubular member 2 is inclinedly welded to the first tubular member 1. In the pressure sensor described above, the axial misalignment tends to become large, because there are two weld portions located outside the housing 10.